Conventionally, a contact lens is provided with an identifying mark in the form of letters and figures, symbols, patterns, etc., principally for easy distinction, at a time of wearing, between the front and back surfaces of the lens or between lenses for the left and right eyes, and/or indicating the specifications and/or maker of the lens, for instance.
Various methods have been adopted for marking the ophthalmic lens with the above-mentioned letters, figures, symbols, and patterns. For example, there are known printing methods, in which marks are transferred on the lens surfaces, i.e., on the back surface (base curved surface) and/or the front surface (front curved surface), by using an ink, which is obtained by dissolving or dispersing a dyestuff such as a dye or a colorant in an organic medium. There are also known laser radiation marking methods, in which desired marks are printed or engraved by using a laser directly on the lens or on a mold and transferred to the lens.
However, with regard to the mark formed by the former printing method, there are anxieties that the dyestuffs of the mark may be flowed off, discolored, or peeled off due to various treatments repeatedly conducted on the lens, such as cleaning of the lens by rubbing and repetitive disinfection.
Meanwhile, the mark formed by the latter laser marking method is not easily readable. In addition, as the mark is made by forming grooves or recesses on the lens surface by the laser radiation, the thickness of the portions of the lens, which portions are subjected to the laser radiation, is inevitably reduced, or the lens material is ablated by the laser radiation. In either case, the mechanical strength of the ophthalmic lens is reduced.
Therefore, there are needs for a method for making silicone hydrogel contact lenses with identifying marks for the user, while still retaining an acceptable comfort level of the marked contact lenses and further providing other benefits for the user.